Spaghetti diagrams, part 2 --

In earlier years of Lawrence Livermore National Laboratory’s spaghetti diagrams, such as the above example from 1976, the ends of the swaths were more like the simpler energy flow diagrams. On the above diagram it’s easier to see that the height of the lines on one side would end up around the height of the lines on the other side than it is on some of the newer versions with oversized boxes that serve as labels. But the boxes are a useful tool, and can let us think about embedding another diagram form — box diagrams — into the spaghetti diagram.

Box diagrams are used for teaching electricity, and were developed by Peter Cheng and David Shipstone in the UK. The picture below is from part 1 (Word doc) of their introductory paper (here’s the Word doc part 2). Since power is the voltage across a bulb multiplied by the current through it, for a simple circuit like that shown in figure a, two boxes of equal size as shown in figure b can represent the power from the battery (the left box) and the power used by the bulb (right box).

Below is a figure from a 1981 article by Howard Hayden (pay article) in The Physics Teacher. If you tilt your head to the right, you can imagine this diagram integrated with the spaghetti diagram. You can also think of is as a box diagram, where the energy sources on the “left” (top) are matched up with the end use loads on the “right” (bottom). This figure includes the electric utilities, just like the spaghetti diagram. And while it doesn’t graphically allocate that 21% “low grade heat” from electricity generation, it does say that industry would go from 27% to 37% of total energy use if “corrected by utilites’ waste heat,” and residential/commercial would go from 25 to 37%. (Those numbers are for 1978). Transportation is unassigned, and not grouped by vehicle.

If we “zoom in” on the Residential & Commercial box we can break it down further into how energy is used in each place. These figures are from the 2008 American Physical Society report Energy = Future: Think Efficiency.

Residential Energy End Usage

Commercial Energy End Use

If we show the lost heat and CO2 for each of these individual pieces, perhaps we can motivate people to think about their actions more as part of a much larger whole. We can also show the benefits of taking Effective Actions for saving energy.

The interesting thing about stacked bar charts versus pie charts is that the bar charts have an added layer of quantification — we can compare bars to one another by making them quantitative. Here’s a graphic from the National Academy of Science’s What you need to Know about Energy booklet that gives a feel for the difference between the two types. The pie chart is for fractions of 100%, while the bar chart can be scaled as needed.

Once we quantify that bar chart, we can start to compare it to other bar charts. In fact, we could localize American data to compare with the diagrams in David MacKay’s great book, Sustainable Energy — without the hot air. MacKay methodically stacks up all of the UK’s potential renewable energy sources (right green stack in diagram below), and compares it to all of the UK’s energy use (left red box), looking at both on a per capita basis.

To really drive the comparison home, we can look at the energy budgets of the developing world versus the developed world, as done in the image below. The question is: How much energy for how many people? It’s a nice presentation of world poverty and wealth scenarios. (This image, and the spaghetti diagram at the top of this post, are from a 1985 paper by Robert Socolow.)

If we mix spaghetti diagrams with box diagrams, we might call them “spaghetti box” (or “Sankey box”) diagrams. It gives us a chance to see the big picture in a visual, semi-quantitative way for a conceptual overview, and become quantitative, especially when zooming in on personal energy use (the idea behind wattzon.com). The spaghetti follows where energy’s coming from, how it’s being used, and areas where we might “reject” less energy. This is a refinement of Saul’s electricity grid stacked bar diagram that could help demystify circuits and make power a much more central quantity in electricity education.